The invention concerns a device for measuring the tire pressure in a pneumatic tire of a vehicle by means of a measurement value sensor, which is acted upon by the tire pressure, at the rim base of a rim receiving a tire valve, for the pneumatic tire, outside which a receiver is associated with the measurement value sensor, wherein connected to the tire valve which has a retaining nut is an electronics or signal housing which is associated with the rim base and which has base bar portions as well as an electronic sender means as the measurement value sensor for the tire pressure. The signal housing is connected to the tire valve by a hollow screw engaging into the valve bore and is adjustable with respect thereto.
DE 37 34 053 A1 to the present applicants describes a device for measuring the tire pressure in a pneumatic tire of a vehicle. A folding bellows arrangement is disposed in the pneumatic tire in a direction of movement which is approximately parallel to the axis and is connected to a permanent magnet which is displaceable in parallel relationship with the axis in dependence on the tire pressure at the outside of the tire and which changes its measurable position, in the event of deviations from the normal tire pressure. An electronic component is proposed as a stationary pick-up means outside the pneumatic tire. The electronic component, by virtue of the so-called Hall effect, respectively produces a voltage perpendicularly to a flow of current and a magnetic field. The above-mentioned Hall effect is based on the consideration that, in electrical conductors which are disposed in a homogeneous magnet field and in which an electrical current flows perpendicularly thereto, a voltage difference occurs, perpendicularly to the magnetic filed and perpendicularly to the current. The magnitude of that effect is dependent on the conductor material and is characterized by the respective Hall constant.
Practice has shown now that, in the case of the measurement value sensor which rotates about the axis of the wheel, as a consequence of frictional forces, caused by the centrifugal force which occurs, as between the folding bellows means or the holder of the permanent magnet on the one hand and the pressure tube on the other hand, the axial movement of the permanent magnet, which is required for measurement purposes, can be disturbed, a hysteresis effect occurs. The latter impedes fulfilment of the demand for a linear relationship, which is independent of speed of rotation, between the tire pressure and the movement of the measurement value sensor.
In order now to simplify fitting the measurement value sensor in the region of the rim and to ensure the operational reliability and security thereof even when the vehicle tire is changed, DE 296 23 466 U1 to the present applicants proposes a device of the general kind set forth. This is delivered to the vehicle manufacturer in parts and put together by same upon assembly.
In consideration of the state of the art, the object of the present invention, in a further development of the wheel module, is to afford a modification to the system for the purposes of simplifying assembly.
That object is attained by the teaching of the independent claim; the appendant claims set forth advantageous developments. In addition, the scope of the invention embraces all combinations of at least two of the features disclosed in the description, the drawing and/or the claims.
In accordance with the invention, provided at the inside or in the interior of the retaining nut is a projection as a desired-rupture element. This can be associated as a possibly separate installation component with the inside surface of the retaining nut and is preferably in the form of a leg or flange extending around the retaining nut at the inside surface thereof. In addition, the base bar portions of the signal housing are pressed by the hollow screw against the rim base.
In accordance with a further feature of the invention, the surface pressure between the screw head and the electronics housing is so selected that, upon actuation of the retaining nut, the torque rises to such an extent that the inwardly disposed web or flange is sheared off when a given torque, between about 3 Nm and 6 Nm, is exceeded, by the bolt screw thread. Advantageously the torque is so selected that the hollow screw is tightened before the web or flange is sheared off by rotating the valve.
In addition, it has proven to be advantageous for the screw head to be held in positively locking relationship to prevent rotational movement thereof in the signal or electronics housing, For that purpose, the screw head has at least in part a polygonal periphery which bears snugly in positively locking relationship with surface portions against the interior of the signal housing.
In the condition as delivered at the customer, the valve body and the electronic unit are loosely movably pre-assembled with a screw. The retaining nut and the valve cap are supplied separately. Alternatively, the retaining nut can be assembled with a more slender valve cap which is screwed on. For the purposes of fixing the unit, the valve body is fitted through the hole in the rim and the retaining nut is screwed fast until it bears against the rim. For the assembly procedure, that affords a substantial simplification in comparison with present day processes.